Law firms routinely work with documents that contain more personal information than an AI task actually needs. A contract may include names, addresses, signatures, and account details. A litigation file may contain medical records, employment history, witness information, or identification numbers. If a lawyer wants an AI tool to summarize one clause or organize a timeline, sending the entire document can expose far more information than necessary.
PII redaction removes or replaces identifying details before a document is shared with another system. In Canada, the broader term "personal information" is often used. The objective is to reduce unnecessary exposure while preserving enough context for the task.
Redaction is not the same as anonymization
Redaction usually means removing or masking specific details. A client's name might become "[CLIENT NAME]," an account number might be partially masked, and a home address might be removed.
De-identification goes further. NIST describes de-identification as removing identifying information so that data cannot readily be linked to a specific individual. NIST also warns that some de-identified data can sometimes be re-identified when enough remaining details are combined.
That distinction matters in legal documents. Removing a person's name does not necessarily make the document anonymous. A combination of job title, employer, location, dates, medical history, or unusual factual details may still point to one person.
For AI use, the safer question is not "Did we remove the name?" It is "Could the remaining information still identify the person, and does the AI need those details?"
Start with the purpose of the AI task
Before redacting anything, decide what the AI is supposed to do.
If a lawyer wants help improving the wording of a clause, the model may need the clause and some surrounding context. It probably does not need the client's full identity, signature page, banking information, or unrelated schedules.
If a legal team wants to summarize a witness interview, the model may need the sequence of events but not necessarily the witness's full name, phone number, home address, or date of birth.
The Office of the Privacy Commissioner of Canada recommends using anonymized, synthetic, or de-identified information instead of personal information when the real information is not required for the purpose. It also advises organizations using generative AI to use de-identified information in prompts where possible and to enter sensitive or confidential personal information only when that use is authorized.
Redaction becomes much easier when the team first narrows the task.
Redact more than obvious identifiers
Names, email addresses, and phone numbers are only the beginning.
Legal documents can contain government identifiers, dates of birth, financial account numbers, employee IDs, medical information, photographs, signatures, property addresses, family relationships, case numbers, or combinations of facts that identify someone indirectly.
The Canadian Bar Association's Privacy and Ethics Toolkit notes that personal information can include financial information, employment history, medical information, identifying numbers, and other information about an individual. It also advises lawyers using public AI systems to remove identifying details.
A practical review should therefore look at the document as a whole rather than relying on a search for names.
Preserve structure when the AI needs context
Redaction does not always mean deleting information completely.
A placeholder can preserve the structure of a document. For example:
"Sarah Chen signed the agreement on March 12" could become "[EMPLOYEE A] signed the agreement on [DATE]."
If several people appear throughout the document, consistent labels such as "[CLIENT A]," "[WITNESS 1]," and "[EMPLOYEE 2]" allow the AI to follow relationships without receiving the real identities.
For some tasks, dates or locations may matter. Instead of deleting them automatically, consider whether they can be generalized. An exact birth date could become an age range, or a street address could become a province if the precise location is not relevant.
The goal is to preserve the information needed for analysis while reducing information that creates privacy or confidentiality risk.
Remember that client confidentiality is broader than PII
A legal document can be highly sensitive even after every personal identifier is removed.
The Law Society of Ontario requires lawyers to hold in strict confidence information concerning the business and affairs of a client acquired during the professional relationship. The Canadian Bar Association also distinguishes confidentiality from privacy and privilege, noting that confidentiality can protect information more broadly than personal information alone.
That means redaction is only one safeguard. A contract may contain confidential pricing, legal strategy, settlement positions, intellectual property, or transaction details that still should not be entered into an unapproved AI tool.
Before uploading a redacted document, the firm should still confirm that the AI system is approved for the type of information involved.
Check the finished document before uploading it
Automated redaction tools can help, but they should not be assumed to catch every identifying detail.
Review the redacted version separately from the original. Look for information in headers, footers, comments, tracked changes, file names, tables, appendices, and metadata. A document can look clean on the page while still containing sensitive material elsewhere.
For higher-risk matters, a second review may be appropriate before the file reaches an external AI system.
Build redaction into the workflow
Redaction works best when it is a normal step rather than something lawyers remember only for unusually sensitive files.
Create simple rules for which categories of information should be removed, which placeholders to use, when a second review is required, and which AI systems are approved for redacted legal material. Staff training should include realistic documents and examples rather than only general instructions about protecting privacy.
PII redaction can make legal documents safer to use with AI, but it should not be treated as a guarantee that the document is anonymous or risk-free. The useful approach is to minimize the information, preserve only the context the task requires, check for indirect identifiers, and remember that client confidentiality can remain even after personal information has been removed.
Redaction has one hard constraint: it only protects a document if it happens before the document is shared. Once a prompt is submitted, it cannot be recalled, so a name, a file number, or a medical detail left in a pasted clause is already with the tool. This is the principle Sanitized Ai is built on, catching and redacting personal information and other sensitive client details in legal documents before the prompt reaches the tool, so lawyers keep the context they need without sending the identifiers they do not.
This quarter, choose one recurring legal AI task, such as clause rewording or witness-interview summaries, and write down which categories of information to remove, which placeholders to use, and when a second review is required. Test those rules on a few realistic documents before they become the standard. If you want to see what redaction before submission looks like in your own workflow, request a demo.